In mobile communication systems, a frequency-hopping technique may be used. For example, the transmit-receive frequency changes dynamically when using frequency division. In applications like ultra-wide band (UWB), a change of frequency and/or a change of channel should be completed within nanoseconds. However, in a phase-locked loop a settling process on a new channel usually takes several microseconds, so that a single PLL is less suited for frequency synthesis for a frequency-hopping system.
Conventional fast frequency-hopping synthesizers generate a basic frequency using conventional PLL techniques. The signal thus generated is mixed with a low-frequency signal in a mixer and is filtered subsequently. The basic frequency can be varied by an offset, achieving different frequency channels. The low-frequency signal can be generated using a periodically addressed read-only memory (ROM) with subsequent digital-to-analog conversion.
As an alternative, conventional frequency-hopping synthesizers may use a single-sideband mixer architecture.
The generation of additional low-frequency signals consumes more power and occupies additional chip area when implemented with integrated circuit technology.